Download ii. 1-wire interface

An Identifying and Authorizing Application Using
1-Wire® Technology
Eugen DIACONESCU, PhD
Cristian SPIRLEANU
University of Pitesti
Pitesti, Romania
[email protected]
General Serv IT
Pitesti, Romania
[email protected]
Abstract—This paper presents a hardware and software
application using the 1-wire technology. The application has
several components: 1-wire network of iButton® type devices,
addressable switches, serial EEPROM memories, the software
package developed for Windows operating system.
The
application achieves several goals: 1-wire network interrogation,
data processing, implementation of several control functions of
identification and authorizing type. The solutions given have
advantage of the hardware simplicity, which is specific to the 1wire technology, and high efficiency in building complex network
architectures. The practical usefulness of the application
presented is to be found in the industrial field, in intelligent
building, in alarm and anti-burglary systems, in sensor networks,
etc.
Keywords - 1-wire network, iButton®, addressable switch
I.
INTRODUCTION
In the domain of identification traditional technologies are
used, such as the bar codes applied on surfaces, the magnetic
stripes, the chip cards, and the RFID labels. To these
technologies can be added another successful one, which is
based on the 1-wire communication network.
The 1-wire technology has emerged from the evolution of
the semiconductor technology. It was designated to some
specific applications to substitute the identification by paper
label based on bar codes for the electronic circuits. Dallas
Semiconductor was the first producer which developed a large
used automated identification through attached chips to
objects or persons.
The iButton® technology belongs to the category of the
technologies of identification by touching. The simplest
identification method can be realized by using a microsystem
with two external electrical wire connexions: signal and
ground. The general advantages of iButton® versus others
systems are: the reading without expensive optical devices, the
hundredfold increased storage of data as compared to a bar
code, the identification through a unique serial number
(which can represent a node in a global network of a
practically unlimited dimension), the content of the iButton®
chip can be modified while it is attached to the object, it can
allow over 1 milion programming cycles of EEPROM
memory, it has a good adaptation to hard environments
(corrosion, shocks, vibrations, etc.), reading and writing are
done by means of small-sized portable having a reduced
energy consumption, it has multifunctionality by integrating,
into the same device, another functions (temperature and
humidity sensors, etc.).
II.
1-WIRE INTERFACE
The 1-wire concept links the master initiating
comunication and the slave autosincronising with master
signals. The time logic of master and slave must measure and
generate digital pulses of diferent lengths.
In the idle state, the 1-wire bus is in ”1” logical state and
presents a way of high impedance for the applied operating
signals. Any connected device to bus must capable to pull
down 1-wire bus in the ”0” state at the desired time using an
output of type open-colector. To stop a data transfer in
progress, the bus must to pass in idle state from which the
transaction can continues later.
A. Operating tension levels
The most 1-wire slave devices work in [2,8V – 5,25V]
range. With few exceptions, the 1-wire device do not have
supply pins; they take the energy from the 1-wire bus (so call
“parasitic supply”) or from an embedded battery (at some
iButton® devices). Parasitic supply uses an on-chip capacitor
(≥ 800pF) and a diode serialized with a resistor for the take of
energy from 1-wire bus when tension on bus is higher as the
tension on capacitor.
For a correct functioning of “parasitic energy”, some
conditions specified in data sheets (VPUP, RPUP, tREC, etc.) must
realized. The values of restoration time are given for a
network with one slave. For networks with more slaves, the
restoration time need to be extended, or the value of pull up
resistor can be reduced [AN3829].
B.
Additional energy
As a rule, “parasitic energy” assures enough energy for
communication (addressing, reading, and writing). More
energy is necessary for writing in some devices, among which
iButton® devices with EEPROM memory. This energy must
be delivered at specified times from protocol, when 1-wire bus
is idle [AN4225].
C. 1-wire® transmission speed
The former 1-wire devices and the master UART based
circuits communicate at the 16.3kbps speed, named now
“standard speed”. The module “overdrive” (142kbps for
iButton®) was added at almost any produced devices. It
reduces the necessary time for reading memories of type 64kbiButon by multiplying 10 times the speed performances.
D. 1-wire® bus synchronization
The technical documentation use two styles for the
description of realized time sequences on the bus: traditional
and new, with small particularities. In the next we will referee
to the new style.
The communication 1-wire® start with a reset cycle (or
“presence detection”), figure 1 [1, 2]. To determine the output
from idle state, the tension on 1-wire bus must to move down
from VPUP below threshold level VTL. To pass from active
state into idle state, the voltage must increase from VIL MAX
over the VTH threshold. The necessary time for this increasing
is noted in figure 2 with “ε”, and his duration depends on the
pull-up resistor RPUP and the attached capacitor to the 1-wire
network. The VILMAX tension has significance for slave when
determines a logical level, and not for shareholding any event.
A duration of 480μs or larger of tRSTL makes device to
leave Overdrive Mode and to return at standard speed. If a
slave is in the Overdrive Mode and tRSTL is between 80μs and
480μs, the device will reset, but communication speed is
undetermined.
tMSP
Reset Impuls MASTER Tx
Presence Impuls MASTER Rx
ε
VPUP
VIHMASTER
VTH
VTL
VILMAX
0V
tF
tRSTL
tPDH
Resistor
Master
Slave
tPDL
tREC
tRSTH
Fig. 1 The master reset the bus and detect the possible connected slaves
The master enters in receiving mode after it releases the
line. As a consequence, the 1-wire bus is pulled down at VPUP
by the pull-up resistor. After passing the threshold VTH, the
slave waits a time tPDH and then sends a presence pulse by
pull-down of the line for a time tPDL.
To detect a presence pulse, the master must test the logical
state of 1-wire line after a minimum elapsed time tMSP. The
window tRSTH must be at lest the sum of tPDHMAX, tPDLMAX and
tRECMIN. Immediately, after elapsed time tRSTH, the slave will be
ready for data communication.
E. Read/Write time frames
After the ending of reset/presence detection cycle, a 1-wire
slave will be ready for communication using the time frames.
Every time frame carries on a single bit. Time frame for
writing carry on the data from a master to a slave, and the time
frames for reading carry transfers data from a slave to a
master. The definitions of reading and writing frames are
better understand from figures 2 and 3.
A time frame begins with the master pulling down of data
line. Immediately that the voltage level on the 1-wire line
decreases below the threshold VTL, the slave starts its internal
generator, which determines when there is a sampling of data
line while writing frame and the long data validation while
reading time frame.
F. Master to slave
For a time frame of writing “1”, the voltage on data line
must cross in descending the lower threshold V TH before
exceeding the time tW1MAX (figure 2 [1, 2]).
For a writing “0” time frame (figure 4), the tension on the
data line must state below the threshold VTL a time greater
than tW0LMIN. At returning on a high level, after ascending
traversing of the level VTH, a slave needs of a restoring time,
tREC, before will be ready for the next time frame.
Time frame Write - One
tW1L
VPUP
VIHMASTER
VTH
VTL
VILMAX
0V
ε
tF
tRSTL
tSLOT
Resistor
Master
Slave
Fig. 2 The master writes “1” on line
G. Slave to master
A time frame of data reading by master begins in the same
way as a “writing 1” time frame, (figure 3 [1, 2]). The voltage
of low level, on the data line, must remains below V TL until
the reading time tRL will be exceeded. When respond with a
“0”, the slave starts ever since the window time tRL, keeping
data line low; its internal time generator sets when starts this
pulling down and then does to increase again the tension.
When respond with a “1”, a slave don’t keep down the data
line, the tension begins to increase immediately after t RL
exceeding. The sum tRL + δ (rising time) on the one hand, and
tMSR
Time frame Read-Data
VPUP
VIHMASTER
VTH
the internal time generator on the other hand, defines the
sample window of the master, tMSRMIN until tMSRMAX.
From clarity reasons of explanations, the rise time and
descendant time in figures 3÷6 were been presented as having
an exaggerated duration. In reality, as it could be observed
from obtained signal pattern at scope in laboratory for the
DS18X20 device, for the “writing 0” and “writing 1”
sequences, the duration of fronts is more reduced, figure 4.
tRL
Master
sampling
window
VTL
VILMAX
0V
δ
tF
tREC
tSLOT
Resistor
Master
Slave
Fig. 3 The slave writes data on line, “0” or “1”. The master reads the received data from slave
- port microcontroller pins. This pins can be dedicated or
commons (as example a GPIO pin for PIC16F Microchip).
The functioning is at the standard or overdrive speed.
- UART interfaces. They are obsolete in general, but a
new convertor (DS2480B) permits enhancement of transfer
efficiency at the overdrive speed.
- I2C ports of microcontrollers. More types of “bridge”
chips are utilized: DS2482-100,-101,-800 (1 to 8 1-wire
ports).
III.
Fig. 4 Waves patterns of the signals in line
H. Transmission improvement in network
In 1-wire environment, it is possible to have different
noise sources. Depending of physical dimension and
network topology, the reflexions from of ends of wires and
ramifications can ones to others sum or cancel. Such
reflected signals are visible as parasitic impulses (glitches)
or oscillations on 1-wire line.
As a consequence, for improving the performance in
applications of the network, it was realized a new interface
(front-end) which is less sensible at noise, and it was
embedded in the new generation of devices. Added methods
are the filtration and the using of level detection/threshold
with hysteresis.
I.
Attachment at hardware interfaces
1-wire interfaces can be attached to the following types
of interfaces:
DESCRIPTION OF A TYPICAL COMMUNICATION 1-WIRE
The general sequence of signals crossing a
communication line of 1-wire type is presented in figure 5.
The master device sends the Reset sequence connecting data
line to logical “0” for at lest 480μs, then it releases the line
and waits to receive a Presence pulse from the any of
subordinate devices. If a Presence pulse was detected as
response, the master will call the slave address using
“writing 0” and “writing 1” sequences.
ID ROM
Code
Reset
sequence command
ROM
Read/write
Data
Code
Function
Reset
sequence
Fig. 5 Typical sequence of signals in 1-wire line
MSB
CRC (8 bits)
Serial Number (48 bits)
64bits
Type Product Code (48 bits)
LSB
Fig. 6. The identification code of the structure of a device
IV.
RESULTS
The fundamental diagram of a 1-wire network with the
length L in reduced (L<5m) and extended (5<L<125m)
variants are presented in figure 7 and the testbed in figure 8.
1-wire network with
maximum length 5m
1-wire network with
maximum length 125m
Local Power
Master
Master
Master
Master
Local Power
Master
Fig. 7 The structure and the dimensions of a 1 - wire network
Fig. 8 The testbed
The identification and control devices have been
connected and interrogated in a 1-wire network by mean of a
program developed using Visual Studio Net environment.
The application was realised around evaluation kit DS9090
and its graphical interface is presented in figure 9; it has the
following functions: Get device, Poll devices, Get switches,
Poll switches, Get temps, Poll temps, Stop polling. Starting
the application ”1-wire PC App”, in figure 9 appears the
detection of adapter DS9090 connected to an USB port.
Fig. 9 The launching screen of the application after port recognition
To search all devices from 1-wire network, the button
„Get devices” is pressed. In the left window wil be displayed
the founded devices (partial in figure 10), with the following
field information of information for each device:
- Adress, unique code for each device.
- Name, family of the device.
- Description, a summary about type of device, technical
characteristics, and the device functions.
In our application, the following devices are detected in
the 1-wire network:
Fig. 10
1. A temperature measuring digital sensor with a unique
code (270000801CDE47810), from family DS1920, having
the following characteristics:
- measured temperature interval: -55 1000C;
- measuring precision 0.50C in the [00-700C] range;
- displayed resolution 0.50C. For a resolution of 0.10C a
interpolation method is used;
- an auxiliary function permits the setting of temperature
level (max/min) for the generation of alarms in the case of
exceeding of the limits.
2. 1-wire addressable evaluation circuit (unique code
98000003C9E36B1C) from family DS28E4 has an
EEPROM memory of 4k bits and two generating signal
channels.
3.
An
addressable
switch
(code
unique
F4000000664F2412) from family DS2406. The physical
control of an output is realized by intermediate of this type
of device. The characteristic of output channel are 0.4V,
50mA. The EEPROM memory has 1024 bits.
4. A device of type “reader” from the same family
DS1990
as
iButton
devices
(unique
code
EB0000002C8D2681 has the role of valuators for adapter to
permit the using of the evaluating kit DS9090K).
The “Poll devices” command launches the control
routine which interrogates all the connected devices, detects
the authentication type iButton devices and validates the
input code.
When the button “Poll device” is pressed, in the
application window will appear the devices of 1-wire
network, interrogated at the 0.5s period, with the address
field device family (unique code). For the devices of switchaddressable type, the states of channel will be
supplementary displayed (status Ch.0: OFF or ON), and also
the signal level at the channel output.
It can be observed that for the output type addressable
switch having connected a load (even for non-activated
output), the detected level is logical “1” (High).
In our application, the logical level of channel 0 of
device DS2406 is “High” because a load (a LED) is
connected to this output. The period of interrogation is
displayed with the green indicator which intermittently
lights controlled by the interrogation routine, figure 11.
Fig. 11 The working devices after "Poll devices"
In figure 12 is showed the detection of the coupling of a
iButton device by the reading device iButton. In the left
window, a device iButton type is detected, showing his
unique code (7D00000ECB181001) and its family
(DS1990A).
Fig. 12 The display with iButton® devices at the moment of key
connecting
The other device from the same family (Ds1990A)
having the unique code (EB0000002C8D2681) is already
included in the list because it is located into USB adapter,
prior to activation.
When detecting iButton device, the software takes no
decision because the detected serial number differs from the
authentication serial number (written into text-box, below
the “1-wire iButton” label, 1900001044A08301).
In the following, a practical exercise is presented. The
button “Stop polling” is pushed, and the existent
authentication serial number is changed with that displayed,
at the detection of iButton device (7D00000ECB181001).
After writing the new serial number, the iButton “Poll
device” is pushed and the software decision is presented in
figure 13.
One will observe that if the serial number of the
authentication device iButton is the same with serial number
inserted in the text-box, a timed action of the channel 0
output of DS2406 device will be launched (3s).
Fig. 13 The result of “Poll devices” action
The following actions will be realized:
- an activation command of channel 0 will be launched;
- a software timer is started;
- at the end of delay (after 3s) a new command for unactivation of the channel 0 is launched.
Visual effects are: the validation code box lights for a
short time, and the button “Ch.0” lights green for 3 sec. In
the same time, the connected LED at the output of Ch.0 of
DS2406 circuit follows the state of software button “Ch.0”.
For any of “Poll” By pushing button “Stop polling” button
types, the interrogation loop is stopped.
This example can be applied in an application of access
control in buildings.
By pressing the button “Get Switch”, the program
interrogates the 1-wire network and searches only the
devices that apart to device category of “addressableswitch” type. The figure 14 shows the two devices of
addressable switch identified (DS28E04) and (DS2406)
having un-activated channels (OFF).
For monitoring the state of channel 0 (with an
interrogation rate of 0.5sec), the button “Poll switch” is
pressed, so as it is observed in figure 15.
Fig. 14 The result of "Get switch" action
Each device is described by the address/family/number
of channels fields, the state of channel and the logical level
at output.
use of iButton® devices, addressable switches and also
temperature sensors devices.
Fig. 15 The result of “Poll switch” action
In the application has been presented only the state of
channel 0, because the addressable-switch devices with
three pins (TO92) have only one channel (0).
Channel 0 is activated/deactivated with button “Ch.0”.
The command is send for all switches of “switchaddressable” type. Pushing button “Ch.0”, it will be tracked
the LED-state (hardware implementation), the state of
button “ch.0” (software monitoring at distance) and the state
of channel from the list with 1-Wire devices, figure 16.
It will be observed that a delay time (<1s) exists between
the moment of launching a command (action of button
”Ch.0”) and execution of command (turn on/off of greenLED) because of too large interrogation gap (0.5s), and also
necessary time space for processing and transmitting
command to 1 wire device, DS2406.
Fig. 17 The sensor temperature device
The iButton® devices are ideals for applications where
the information is transported by a person or an object. This
is the case of the building access, vehicle, equipment or even
PC computer. The device can be easily attached to another
mobile piece. Some variant of iButton® may be used as
payment tools for parking, automatons for consume
products, transit or small volume acquisition systems. Other
diverse applications of iButton® can be discovered by
searching on the internet.
The 1-wire network tested in our application is intended
to be used at the intelligent buildings (monitoring and control
temperature, humidity, ventilation, open/close status of
access ways, access cards, etc.). Also there are many other
domains for using this 1-wire network: meteorology,
parameter control in embedded systems, vehicle security,
banking cards, sensor networks, etc.).
VI.
[1]
[2]
[3]
[4]
Fig 16 The effect of the pressing button “Ch.0”
Temperature control. The button “Get temp”
interrogates the 1-wire loop searching the device of
“temperature” type, figure 17. A sensor temperature device
is identified with the following fields: address: 27
000801CDE47B10; name: DS1920; description: digital
thermometer for temperature measuring -55 1000C, etc.
The temperature is registered at the moment of searching
device. The temperature is measured with a resolution of
0.50C, and by an interpolation method it can be displayed
with a 0.10C resolution, figure 17.
V.
CONCLUSIONS
This article describes our hardware and software
application of the 1-wire technology which referrers to the
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
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